Johannesburg’s mine dumps look strangely beautiful from a distance. Lustrously yellow in the sun, blazing red at dusk, their huge molehill shapes provide the city with its distinctive skyline.

Up close, it’s a different story. Rasalind Plaatjies has lived in the shadow of a “tailing” – as these piles of mine waste are known – all her adult life. Today, the 62-year-old grandmother from the city’s Riverlea district suffers severe respiratory problems. For 16 hours a day, she is hooked up to an oxygen tank, her lungs debilitated by dust from the waste heap.

“Sometimes I don’t have the energy to get up. I just have to stay in bed and do nothing,” she says. She feels fortunate, though. A number of her elderly neighbours have died from respiratory disease.

Plaatjies is one of tens of thousands in Johannesburg’s impoverished townships who are paying a high cost for the city’s rich mining past. More than 600 abandoned mines surround South Africa’s largest city, with much of their waste now piled up high next to residential communities – most of which are poor and black.

Rasalind Plaatjies has severe respiratory problems. ‘Sometimes I don’t have the energy to get up.’ Photograph: Melusi Nkomo

“During August and September, the dust is terrible. You stop cleaning the floor after a while. It’s just useless,” says Plaatjies.

In the local clinic, respiratory cases such as tuberculosis and asthma are ubiquitous across all age groups, says Musa Mbatha, chairman of the clinic’s civic committee. Rashes and skins diseases are commonplace, too.

“People can’t afford to buy food every day, so they leave the food and it gets contaminated,” Mbatha adds. “The government said that it would do a survey of the health impacts of the mining dust, but until today it hasn’t happened.”

Johannesburg is undoubtedly the most uranium-contaminated city in the world

Dr Antony Turton

An even more dangerous pollutant is lurking in Johannesburg’s mine dumps, however: radioactive waste. According to one university study, an estimated 600,000 metric tonnes of radioactive uranium are buried in waste rock in and around Johannesburg – around three times what was exported during the Cold War.

“[Johannesburg] is undoubtedly the most uranium-contaminated city in the world,” says Dr Antony Turton, a professor at the University of Free State’s Centre for Environmental Management.

“For most of the gold mines, uranium was merely a waste product and therefore dumped without being recovered. Those tailing disposal facilities therefore have a relatively high uranium concentration today,” Turton says.

Without the proper precautions in place, ore-bearing uranium leaches from the tailings and enters as run-off into surrounding streams and wetlands. A similar process occurs in abandoned mines underground, with polluted water seeping through porous rock as the mines flood.

Despite its vast reserves of groundwater, Johannesburg pumps most of its drinking water from Lesotho – more than 380km away – because its own water reserves are too polluted.

A hardened white wasteland stands where plants used to grow. The soil has a pH of 2.67 – more acidic than vinegar

Mine waste is also removed illegally from tailings for use in the manufacture of bricks and for other construction purposes, some environment groups allege. Potentially, the physical infrastructure of Johannesburg could be becoming radioactive as well.

The release of uranium in dust form can be exacerbated by the re-mining of tailings – a process that happens in various locations across the city. The companies involved in this re-mining maintain that they are providing an environmental service by removing waste and depositing it in modern tailings that are better regulated.

David van Wyk, chief researcher at the Bench Marks Foundation, a church-funded non-profit based in Johannesburg, is sceptical about mining companies’ environmental practices. “When the uranium price is very low, the mining companies simply dump it. That’s why the dust is yellow. We call it ‘yellow cake’,” he says.

Bench Marks, which receives support from UK charity Christian Aid, is mid-way through a three-year impact assessment of pollution levels in an around Johannesburg’s Soweto district. By systematically tracking air and water contamination, Bench Marks hopes to provide a scientific basis for the alleged health impacts of the tailings.

A handful of randomised spot-checks reveal the extent of the pollution problem. For example, in a narrow run-off canal immediately opposite Soccer City, site of the 2010 Fifa World Cup final, van Wyk picks out the colours along the bank: red for iron, white for sulphur, green for copper, yellow for uranium, and so on.

The pH level measures 4.6: within the range for acid rain (neutral water has a pH level of 7). The figure for Total Dissolved Solids (a measure of minerals, metals and other insoluble materials), meanwhile, is 2,000 parts per million – four times higher than the guideline amount in the US.

A street in the Riverlea township. Rainy season causes polluted water from Johannesburg’s mine dumps to flood into local water courses. Photograph: Oliver Balch

“When it floods, this just goes straight into the river. You’d expect the government to check that the mine water isn’t spilling into local watercourses, but they are not,” van Wyk says. “This is happening in the centre of South Africa’s largest city, close to the Department of Environmental Affairs’s main office. If they can’t regulate so close to their headquarters, just imagine how bad it is elsewhere?”

A few miles away, the township of Diepkloof in Soweto catches the run-off from several large tailings. A few hundred feet from residents’ front doors, a run-off canal has burst its banks. A hardened white wasteland now stands where reeds and plants used to grow. A lifeless stream runs next to it. The soil’s surface, meanwhile, is scuffed with the imprint of cattle hoofs and children’s feet. The soil has a pH of 2.67 – more acidic than vinegar.

Just downstream, an evangelical church carries out full-immersion baptisms in the water, points out Charles van der Merme, a representative of the non-profitMining and Environmental Justice Community Network of South Africa. “They think they are cleansing themselves,” he says. “Who knows? Perhaps it kills all the devils in you.”

“It’s totally inappropriate that communities live on waste that is widely accepted to be toxic and radioactive,” says Mariette Liefferink, chief executive of theFederation for a Sustainable Environment.

It’s totally inappropriate that communities live on waste that is widely accepted to be toxic and radioactive

Mariette Liefferink

According to the Chamber of Mines, all current re-mining meets regulations that prohibit radioactive contamination run-off. The problem lies instead with the owners of historic dumps that “cannot be traced or are not in a position to take responsibility for the required remedial measures,” the industry body states.

For its part, DRD Gold, which is currently involved in secondary gold mining of the Diepkloof tailing, says it is “constantly searching for new methods of dust suppression”. Among the measures it is currently using are netting and vegetation growth. Neither were visible on the Diepkloof dump, however.

According to the company, DRD Gold spends up to R48m (£2.5m) a year managing the environmental impacts of its operations, which stretch over 70km around the city. “Any [pollution] readings that exceed the legal limits are automatically flagged and managed in terms of an automated action list”, a company spokesperson stated.

For those living in the shadow of the dumps, a sense of hopelessness pervades. Sixty-two-year-old Stella Adams, a long-term resident of Diepkloof, has written to numerous government departments to complain about the high levels of dust in her home. “All I am asking for is some vegetation [on the tailing]. I am just asking for the most basic thing,” she says. “But nobody has ever given me a hearing … so I have lost hope.”

Adams’s grandson developed asthma shortly after moving into her home six years ago. Her sister recently died from lung cancer, despite never having smoked. Adams assumed the cancer was hereditary, so made no mention to doctors of the nearby tailing. “Now I wonder if it had to do with the mine after all.”

In the Soweto district of Meadowlands, for example, hundreds of government-built houses are currently going up in the Fleurhof extension community. Mine dumps tower above the development on all sides. Yet, despite knowing the dangers, 41-year-old Charles van der Merme says he would move there “in a flash”.

One of the millions of unemployed residents in this city of 4.8 million, he and his family currently live with his parents-in-law in the township of Riverlea. “I applied for a government house in 2000 and I’m still homeless,” van der Merme says. “Despite all the ills from the mine dumps, I would like a house of my own. Where else can I go?”